Infrared Spectroscopic And Theoretical Calculation Studies On Noncovalent Nitrobenzene Anion Cluster Tagged By Argon

Noncovalent interactions（NCIs）have been widely explored in biomolecules and clusters,as well as they play a significant role in environmental monitoring and molecular recognition.In this thesis,Ar-tagged nitrobenzene anion clusters,NB_n（Ar）^-（n=1,2,3）,were prepared and characterized using infrared photodissociation spectroscopy combined with time-of-flight mass spectrometry.Quantum chemical calculations were carried out to reveal the nature of NCIs in NB_n（Ar）^-（n=1,2,3）clusters.The main results include in the following three aspects:（1）The infrared spectrum of NB（Ar）^-in the range of 900-3300 cm^-1 was assigned by DFT calculation.Three C-H stretching vibrations of 3006.5,3048.6 and 3084.5cm^-1 were resolved for the first time.The results indicated that the relative energies of the five possible NB（Ar）^-were all less than 2.0 kcal·mol^-1as well as the positions of argon demonstrated almost no influence on the vibrational frequencies at B3LYP/def2-TZVP level,and the calculated spectra are all in better agreement with the experiment.（2）Based on the infrared spectra of NB₂（Ar）^-,26 isomers of NB₂（Ar）^-were optimized at the M06-2X/def2-TZVP level.They were classified into three types of double hydrogen bonded（DHB）,antiparallelπ-πstacked（APS）and T-typed（TS）based on the sites of NCI,and the energy order is DHB1<TS1<DHB2≈APS<TS2.The calculated spectra of APS conformation were in much better agreement with the experiment as well as the experimental spectrum was identified.Topological analysis and SAPT calculations indicated that NB₂（Ar）^-is mainly an antiparallel stacked structure dominated by O=N···πandπ-πinteractions,and both dispersion and electrostatic interactions corporately stabilized the structures.The singly occupied molecular orbital（SOMO）indicates that the negative charge is mainly distributed on only one NB section rather than equally distributed on both NBs.（3）We optimized and obtained 26 isomeric NB₃（Ar）^-at M06-2X/def2-TZVP level,in which four types of characteristic NCIs included C-H···O andπ-π,as well as coupled interactions,such as C-H···O+π-π,C-H···O+C-H···π.Y-typed,triangular and planar geometries dominated by C-H···O interactions,their energy differences are relatively larger.π-πor C-H···πwould increase stability of structures.The calculation showed that the calculated spectra of planar geometry was in much better agreement with experiment.Due to the relative complexity of the experimental spectrum,planer and Y-typed isomers may co-exist,as well as the strong absorption peaks of 3018.5 and 3032.6cm^-1 observed in the experiment are attributed to C-H···O interaction of both configurations.SOMO analysis indicates that the negative charges of both configurations are distributed on one NB.